Desoye G, Hartmann M, Jones C J, Wolf H J, Kohnen G, Kosanke G, Kaufmann P
Department of Obstetrics and Gynecology, University of Graz, Austria.
Microsc Res Tech. 1997;38(1-2):63-75. doi: 10.1002/(SICI)1097-0029(19970701/15)38:1/2<63::AID-JEMT8>3.0.CO;2-V.
The insulin receptor gene is constitutively expressed, so the presence of insulin receptor proteins might be expected on all mammalian tissues, with the plasma membrane as the predominant site of receptor location. Results reviewed here indicate that insulin receptors are also present in all placental tissues and the placenta's progenitor tissues and cells, i.e., oocytes, spermatozoa, and preimplantation embryos, in most of the species studied. Receptor densities, however, vary among individual cells and cell types and at various developmental stages. Three aspects deserve emphasis. 1) In human placenta, the insulin receptor distribution pattern is characterized by a spatiotemporal change between first trimester and term. At the beginning of pregnancy, insulin receptors are found predominantly on the maternal side (apical membrane of syncytiotrophoblast, low density on cytotrophoblast); at term, however, they are on the fetal side (lining the fetal vessels). This suggests that, in the first trimester, maternal insulin regulates insulin-dependent processes, whereas, at term, it must be fetal insulin mainly controlling these processes. 2) The majority of insulin receptors is expressed on structures that are currently assumed to drive placental growth, i.e., syncytial sprouts and mesenchymal villi in first-trimester placentas and fetal endothelium at term. Therefore, we hypothesize a growth-promoting function, among others, of insulin on the placenta. 3) At present, no histologic evidence is available to demonstrate insulin receptors in structures commonly associated with receptor-mediated endocytosis. Whether placental insulin receptors are internalized, therefore, awaits clarification.
胰岛素受体基因是组成性表达的，因此可以预期在所有哺乳动物组织中都存在胰岛素受体蛋白，其主要位于质膜上。本文综述的结果表明，在大多数研究的物种中，胰岛素受体也存在于所有胎盘组织及其祖细胞和细胞中，即卵母细胞、精子和植入前胚胎。然而，受体密度在个体细胞、细胞类型以及不同发育阶段之间存在差异。有三个方面值得强调。1）在人类胎盘中，胰岛素受体的分布模式具有孕早期和足月时的时空变化特征。在妊娠开始时，胰岛素受体主要位于母体一侧（合体滋养层的顶膜，细胞滋养层上密度较低）；然而，在足月时，它们位于胎儿一侧（衬于胎儿血管）。这表明，在孕早期，母体胰岛素调节胰岛素依赖的过程，而在足月时，主要是胎儿胰岛素控制这些过程。2）大多数胰岛素受体表达于目前认为驱动胎盘生长的结构上，即孕早期胎盘的合体滋养层芽和间充质绒毛以及足月时的胎儿内皮。因此，我们推测胰岛素在胎盘中除其他功能外还具有促进生长的功能。3）目前，尚无组织学证据表明在通常与受体介导的内吞作用相关的结构中存在胰岛素受体。因此，胎盘胰岛素受体是否被内化尚待阐明。
